Area sensor but line scan
Posted 01 August 2012 - 03:53 AM
Posted 01 August 2012 - 11:42 AM
I have compared several different scanners: Oxberry, Northlight, Arriscan, Director, Spirit4K, Scanity.
Posted 01 August 2012 - 12:49 PM
Posted 01 August 2012 - 11:47 PM
Posted 03 August 2012 - 04:12 AM
A line scan sensor is almost just what it says, a single line of pixels, although in reality some will actually have multiple lines for RGB and for intensity enhancement by having say 9 lines with the total charge being added up to increase sensitivity.
Full frame sensors fall into two main types, those with a rolling shutter and those with a global shutter. Although definitely not exclusively, the former shutter type are usually seen on CMOS sensors, the latter on CCD sensors.
Obviously with a line scanner, the image and sensor have to move relative to each other to effect the scan and they have to be tightly locked together otherwise there will be some vertical weaving.
For telecine, either full frame sensor shutter type can be suitable, but depends on the lighting design and the film advance mechanics. A rolling shutter kicks off exposure on the first line, then a few microseconds later on the second line, etc. The actual starting and stopping of the exposure will vary down the frame, so if the subject moves, image distortion will occur. For example, a rotating fan blade will appear to bend. A stationary frame in a film gate will not have this problem of course, but a continuous transport system will have an uneven exposure problem if used with a rolling shutter camera.
My own RGB lighting design uses a constant current through the LEDs during the exposure period. Actual exposure is adjusted by varying the RGB flash lengths in order to get close to full pixel saturation on all three channels so as to utilise the maximum useful dynamic range from the sensor. I use this method because if the current is varied through an LED the light colour frequency changes, making constant colour balanced exposure more difficult. Also it is easier to switch LEDs on and off with a varying period and fixed current than it is to vary the current with fixed period. Downside is that rolling shutter sensors are no good for this type of lighting design.
On the plus side for rolling shutter designs are that they are generally cheaper and have faster frame rates.
Sorry for the long post, but hope it gives some food for thought about how you want to achieve the lighting system and film transport and how this will link with the sensor type.